The invention relates to a system and a method for inserting a weft thread into a shed of an air jet weaving machine.
In an air jet weaving machine, the weft thread which is drawn off from a thread store is accelerated by main and tandem nozzles and inserted into a shed, in which it is further transported by so-called auxiliary or relay nozzles. In conventional air jet weaving machines the relay nozzles are switched on and off by a pre-selected profile which is firmly connected to the rotation of the main machine shaft. It is left up to the weaving master to ideally adapt this profile for a definite article, with more attention generally being paid to the cloth quality than to the air consumption.
In the specification EP 0 554 222 A1 a method is described for the regulation of the weft insertion for a jet weaving machine with a plurality of weft thread monitors which are arranged in the shed in order to be able to determine the time point at which the front end of an inserted weft thread arrives at the location of a weft thread monitor. In the described method the measured time point is compared with a predetermined reference arrival time and the blown-in compressed air of the auxiliary nozzles or groups of auxiliary nozzles which are arranged ahead of or after the weft thread monitor is modified as a result of the comparison of desired and actual values; i.e. the auxiliary nozzles are supplied with low, normal or increased pressure. In the event of a premature arrival the blowing or ventilation time of the auxiliary nozzles can also be shortened in order to delay the weft thread.
The method which is described in EP 0 554 222 A1 is relatively complicated and expensive, since it requires three separate compressed air supplies for the auxiliary nozzles. Furthermore, the simultaneous charging of a plurality of groups of auxiliary nozzles admittedly permits a careful acceleration of the weft thread, which is however associated with a drastically increased consumption of compressed air. In addition, the arrangement of a large number of weft thread monitors in the shed is problematical, since the former damage the warp threads and can thereby influence the cloth quality.